1. Field of Invention
The invention pertains to a method of estimating rotor inertia and, in particular, to a method of instant estimation of a load rotor inertia in an AC servo driver.
2. Related Art
The basic structure of an AC permanent synchronous motor is similar to the conventional synchronous motor. The stator side has a three-phase coil set and the rotor side has a permanent magnet to generate a magnetic field. It does not have a magnetic field excitation circuit, sliding ring, or electric brush. It has the advantages of a high power-volume ratio, high efficiency, and low torque vibrations. Therefore, it is ideal for applications of the drivers in a precision servomechanism, such as a machining mechanical platform with a high precision and a high response speed.
Among the widely used servo control systems, the rotor inertia of a load is an important parameter in the servo design. This parameter has to be accurately estimated in order to make accurate controls of the servo.
Due to the rapid development of digital signal processors, the AC servo drivers have the trend of being intelligent, enabling the AC servo driver to understand the changes in itself and its environment. By intelligence we mean that there are fewer human settings so that it becomes much easier for users to manipulate.
In order to obtain a truly intelligent AC servo driver, the rotor inertia has to be accurately estimated. Some driver designs take the load rotor inertia as an input from the user. This method is less flexible. If users may not know what the load rotor inertia means, then it is difficult for the product to compete with other intelligent products.
Therefore, it is of great importance to provide an estimation method of the load rotor inertia, so that the servo can truly achieve the goal of intelligent operations.
In view of the foregoing, an objective of the invention is to provide a method of instant estimation of the rotor inertia of a load rotor. The rotor inertia of a controlled motor driven by a drive motor is estimated instantly so as to adjust the output of the driver motor, thereby achieving the goal of instant estimation and accurate control.
The disclosed method compares a model system and an actual system to obtain a relative signal. An adaptive filter and the Least Mean Square (LMS) Rule are employed to obtain the parameter of the controlled object.
According to the disclosed method, a motor mechanics control circuit is taken as an ideal model, whose rotor inertia is known. Its speed controller output is one of the input signals for the adaptive filter. The output of a drive motor speed controller in a coupled system and the output of the model motor speed controller are compared to give a deviation quantity as the ideal signal of the adaptive filter. The rotor inertia of the load is then estimated by the adaptive filter using a predetermined algorithm.
To achieve the above objective, the disclosed method first determines an input signal and an ideal signal from a servo control system as two input signals for an adaptive filter. The input signals pass through at least one delayer to obtain at least one delay signal. The delay signal is multiplied with the corresponding weight and output by a synthesizer as a weighted output signal. The deviation between the weighted output signal and the ideal signal is then determined and fed back to determine a new weight. This is the disclosed method that uses the LMS Rule to compute the weight of the adaptive filter using the input signals and the ideal signal. From the above parameters, the invention can determine the rotor inertia ratios among the model motor, the drive motor, and the load motor.